This invention relates generally to mechanical equipment shaft sealing devices and more particularly concerns a shaft seal mechanism which seals effectively when a shaft is at rest, and which changes configurations so as to seal effectively but without friction when the shaft is rotating at an operating speed.
Bearings and mechanical seals may be responsible for up to 80% of rotating equipment failures. There is a close relationship between the life of these two critical components. The failure of a mechanical seal may cause the bearings to fail and poor bearing conditions can reduce seal life. It is estimated that only 10% of bearings achieve their minimum design life of from 24,000 to 40,000 hours (3 to 5 years). Rain, product leakage, debris, and wash-down water entering the bearing housing contaminate the bearing lubricant and have a catastrophic effect on bearing life. Very small amounts of water can compromise bearing life. A contamination level of 0.002% water in the lubricating oil can reduce bearing life by as much as 48%. As little as 0.10% water is reported to reduce bearing life by as much as 90%.
Auxiliary mechanical equipment shaft seals, sometimes called bearing isolators or sealing rings, have become increasingly important to modern mechanical equipment, especially for equipment called upon to operate in hostile applications. For example, mechanical power transmission units used in rock quarries are often subjected to highly abrasive dust particles. Elastomeric lip or O-ring shaft seals can quickly wear out and fail in environments such as these. Dust and exterior contaminants cannot be excluded from the interior of the transmission housing by a failed standard sealing device. Nor can oil or other fluids be prevented from leaking out of the transmission devices past a worn lip seal.
To prevent the ingress of corruption and the egress of lubricating fluids, a number of auxiliary or improved primary sealing arrangements and devices have been provided. Some of these sealing devices provide a physical engagement of the shaft and a wiping action while the shaft operates. Other devices provide an interengagement and wiping action between seal parts. But in both such arrangements, the inevitable friction causes inevitable part wear.
For example, lip seals, commonly known as oil seals, are a well-established method of protecting bearing housings from water, dust, chemical or steam contamination. Lip seals normally involve a stationary elastomeric lip or lips touching the rotating shaft or sleeve at an angle so that contaminants are excluded from the housing. While lip seals have a low initial cost, lip seals have a short protection life, approximately 3,000 hours, due to wear of the elastomer or the shaft itself.
Another type of seal is a labyrinth device which contains a tortuous path that makes it difficult for contaminants to enter the bearing housing to degrade lubricant effectiveness. The advantages of labyrinths are their non-wearing and self-venting features.
Some of these commercially successful seal devices do not require any actual physical interengagement of the sealing member parts. Among such devices which have met with considerable commercial acceptance are those disclosed in Orlowski U.S. Pat. No. 4,706,968; Orlowski 4,466,620; Orlowski 4,175,752; Orlowski 4,114,902; Orlowski 4,022,479; and Orlowski 4,832,350. The disadvantages of labyrinth seal devices include higher initial costs than lip seals, and the existence of an open path to the atmosphere that can allow the contamination of the lubricant by atmospheric condensate as the housing chamber "breathes" during temperature fluctuations in humid environments when the equipment cycles on and off.
The hollow O-ring seal disclosed in applicant's patent 4,989,833 provides static sealing action when the shaft is at rest, and non-contact dynamic sealing action when the shaft is rotating. The solid O-ring seal disclosed in applicant's parent application serial number 07/624,881 also provides static sealing action when the shaft is at rest and non-contact dynamic sealing action when the shaft is rotating. However, in some instances, a small percentage of these O-rings have insufficient lift-off from the stator during rotation of the shaft, such that the seal is subject to premature fatigue and failure due to heat and friction.
Therefore, it is the primary objective of the present invention to provide an improved static and dynamic seal for use with machinery having a housing through which a rotatable shaft protrudes, and which provides effective part-to-part contact static sealing action when the shaft is stationary and which provides effective non-contact dynamic sealing action when the shaft is rotating at operating speed.
It is another objective to provide a machinery seal of the type described in which a solid O-ring seal member engages both a seal stator and a seal rotor when the shaft is at rest, but in which the sealing member expands circumferentially so as to disengage from the stator when the shaft rotates at a normal operating speed.
Still another objective is to provide a seal of the type described which will provide a long, trouble-free service life.
To accomplish these objectives, an isolator mechanism is provided for use with a machinery housing and a rotatable shaft protruding through the housing. The isolator mechanism comprises a stator ring affixed to the housing and a rotor ring which is attached to the shaft. The stator and rotor are so shaped that the stator has a male cylindrical surface, and the rotor has a female cylindrical surface located radially outwardly of the stator male surface. A solid, yet stretchably deformable, annular seal member is mounted on the rotor female surface and engages the stator male surface when the rotor and seal member are at rest. However, the seal member is stretched by centrifugal force into a configuration out of engagement with the stator when the rotor and seal member are moving at operating speeds.
Other objects, advantages and embodiments of the invention will become apparent upon reading the following detailed description and upon reference to the drawings. Throughout the drawings, like reference numerals refer to like parts.